Recently, in association with a spread of mobile terminals such as smart phones and tablet terminals, high-speed mobile communications and a diversification of services for various mobile terminals have advanced, and a required communication capacity has been significantly increasing. While a network cloud service using big data has been gradually spreading in a network system, technologies such as a Machine to Machine (M2M) technology, which shares information between industrial machines, an Internet of Things (IoT) technology, which efficiently operates all apparatuses such as industrial equipment/devices and sensors via the Internet, and an edge computing technology, which executes information processing of IoT devices with an edge router in real-time (instantly), have been gathering the attention as considerably important technologies in the industry.
A further high speed and large capacity are indispensable for optical/wireless communications in an access network and a short range communication network at a data center to establish and develop such technologies. From such aspects, studies on the short range communications in the data center and between the data centers, an optical interconnection of an access system network, and a high communication speed and a large capacity in the optical/wireless communications have been carrying out worldwide. High-speed, large-capacity communications technology using Information and Communication Technology (ICT) hardware meeting requests such as low power consumption, low latency performance of a traffic, and a size and a cost of a communication device achieving such specifications are considered to be indispensable.
A study especially gathering the attention in the above-described field includes a study on a semiconductor optical device using Si photonics and the like and a study on an optical integrated circuit integrating a laser and the like using the above-described semiconductor optical device. The above-described studies on the semiconductor optical device and the like have high mutual compatibility with a Complementary metal oxide semiconductor (CMOS) line, which is used for a micro wiring of an LSI, and are considered to be significantly efficient and allow a low cost. Additionally, since the semiconductor optical device and the like ensure integration with the LSI, the semiconductor optical device and the like are recognized as a worldwide important topic of study in terms of achieving an optical integrated circuit that merges electrical/optical communications and allowing microminiaturization and low power consumption.
However, in the case where the above-described semiconductor optical device is mounted to a part of an integrated circuit in the LSI, a large heat caused by the LSI possibly becomes a problem. Since a temperature of a board around the LSI reaches around 80° C. by the heat generation in the LSI, properties of the semiconductor optical device are possibly deteriorated. Therefore, there is an object to achieve a semiconductor optical device that stably behaves and provides high performance even under a high temperature environment.
In contrast to this, for example, Patent Document 1 discloses a technology regarding a semiconductor laser device that can lower a threshold current especially at near a room temperature. Besides, for example, Non-Patent Document 1 discloses a technology that dopes (injects) p-type impurities into a part near an active layer and forms a light emitting element such as a semiconductor laser using a wafer with a structure in which a crystal is grown to improve a temperature property. For example, Non-Patent Document 2 discloses a technology regarding a method that forcibly cools heat generated from a light emitting element such as a semiconductor laser and other optical integrated circuits by a Thermo-Electric Cooler (TEC) such as a Peltier element.
The semiconductor laser disclosed in Patent Document 1 includes an active layer that includes a plurality of quantum-well layers and formed by arranging the quantum well layers and barrier layers alternatively. Among the barrier layers in the active layer, an amount of band discontinuity on a conduction band side between the barrier layer that is interposed by the quantum-well layers and the quantum-well layers is set to 26 meV or more and less than 300 meV, so that an overflow of carriers due to a thermal excitation between the quantum-well layers is intentionally caused to make a carrier density uniform between the quantum-well layers.